With development of communications technologies, new technologies increasingly emerge. Wideband Code Division Multiple Access (Wideband Code Division Multiple Access, WCDMA) is a third-generation wireless communications system that is most widely used at present. How to evolve a WCDMA system to adapt to a user requirement of high speed uplink and downlink data transmission is a most important research subject in the field of wireless communications. Starting from R5, a series of important technologies are introduced into WCDMA to improve uplink and downlink data transmission rates, such as High Speed Downlink Packet Access (High Speed Downlink Packet Access, HSDPA), High Speed Uplink Packet Access (high speed uplink packet access, HSUPA), multiple-input multiple-output (Multiple-Input Multiple-Output, MIMO), and 64 quadrature amplitude modulation (Quadrature Amplitude Modulation, QAM). After a research on several versions, the research on the improvement of transmission efficiency of a wireless channel hits a bottleneck. To meet the user requirement and address challenges from other technologies, a heterogeneous networking manner—a heterogeneous network (Heterogeneous Network, Hetnet) is taken into consideration for the WCDMA system, that is, networking is performed by using a macrocell (a first cell) with a large coverage area and a microcell (a second cell) with a small coverage area. A coverage area of a cell depends on downlink transmit power of the cell. The Hetnet brings the following benefits: a throughput of the cell is increased, and a cost of the Hetnet is lower than that of a homogeneous network (Homogeneous Network, Homonet) networked by using all first cells.
In the Hetnet, to reduce load of the first cell, a user equipment (User Equipment, UE) at the edge of the first cell is allocated to the second cell for scheduling, and such a practice is referred to as range expansion (Range Expansion, RE). Before RE is performed, the UE sets the second cell as a serving cell only when a geometry factor (Geometry factor) of the second cell is greater than a value (generally 0 dB), and then the UE can be scheduled by the second cell. After RE is performed, the value is generally set to be relatively small (for example, −6 dB), that is, when the Geometry factor of the second cell measured by the UE is −6 dB, the second cell is set as a serving cell, and then the UE is scheduled by the second cell.
However, after RE is performed, an original first-cell UE is changed into a second-cell UE, but a second-cell Geometry factor in an RE region in which the second-cell UE is located is quite low (for example, −6 dB to 0 dB). Therefore, downlink channel quality of the second-cell UE is extremely poor. This is because the RE region in which the second cell UE is located is originally at the edge of the first cell, and a signal from the first cell is strong interference signal for the second-cell UE in the RE region. Therefore, the second cell can only schedule small downlink data packets for these UEs.
In the prior art, the basis of cell pilot measurement is as follows: when Ec/Io of a pilot of a cell is greater than −20 dB, it is considered that the cell is detected by a UE. Ec is energy per chip, and Io is a total power spectrum density at a receiver, including external interference (interference from a neighboring cell and thermal noise) and a signal of the receiver. When Ec/Io is small, Ec/Io may be approximately equal to Ec/Ioc because the signal of the receiver is weak, where Ioc is a total interference power spectrum density at the receiver.
A range of the RE region is restricted by Ec/Io, of a pilot of the second cell, detected by the UE; according to a protocol, when Ec/Ioc, of the pilot of the second cell, detected by the UE is about −20 dB, it is considered that the UE detects the second cell. Therefore, when Ec/Ior of the pilot of the second cell is −10 dB, a geometry factor Ior/Ioc corresponding to Ec/Ioc is generally calculated as follows: Ior/Ioc=Ec/Ioc*Ior/Ec=−10 dB, where Ec is energy per chip, Ior is a total transmit power spectrum density at a transmitter, Ioc is a total interference power spectrum density at a receiver, and Ior/Ioc is the geometry factor. In other words, RE can reach at most a place in which a geometry factor of the second cell is −10 dB. This measurement method greatly limits the expansion range, and achieves a quality measurement result with low precision for the second-cell UE in the RE region.